Methods For Providing High-Surface Area Coatings To Mitigate Hydrocarbon Deposits On Engine And Powertrain Components

ABSTRACT

Provided are methods related to preventing hydrocarbon residue buildup in engine, exhaust-gas-system or powertrain components. Prevention is achieved by applying coating of a mixed metal oxide via a suspension plasma spray.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) to Provisional U.S. Patent Application No. 61/472,319, filed Apr. 6, 2011, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The invention relates generally to the field of combustion engines, and specifically to coatings for preventing hydrocarbon residue buildup on engine, exhaust gas system and powertrain components.

BACKGROUND

Internal combustion piston engines with carburetor or fuel injection usually have several cylinders, and one or more axially-moving pistons enclose a combustion chamber where combustion of a fuel-air mixture occurs.

A pervasive problem with these internal combustion engines is the formation of carbonization residues from unburnt fuel and/or lube oil. These residues are bituminous and, in part, highly complex mixtures of hydrocarbons. The residues are deposited and accumulate on various engine and powertrain structural components. This includes valves, piston surfaces, intake ports, injection nozzles, and the upper surface of the combustion chamber. These carbonization residues may accumulate to such an extent, especially on intake valves, that they produce undesired changes in the fluid dynamics or closing behavior of the valve. Carbonization residues can also have very negative effects on other component surfaces of the combustion chamber (e.g., the piston working surfaces).

Furthermore, known ways of applying coats have not been satisfactory. For example, air spray techniques have been used. However the coatings formed from air spray are not durable. Conventional plasma spray techniques generally provide inactive coatings, and it can be difficult to apply precious metals using conventional plasma spray. Thus, there is a need for a new technique of applying coatings, particularly those that can prevent the formation of carbonization residues.

SUMMARY

Embodiments of the invention pertains to methods for applying a coating of mixed metal oxides comprising at least two of Al, Ti, Ce, Pr, La, Y, Nd, Zr and Mn. Specific embodiments pertain a coating comprising a mixture of Al, Ce, Zr, La, Pr, and Pd.

Accordingly, one aspect of the invention relates to a method of applying a coating to an engine, exhaust-gas-system or powertrain component, the method comprising suspension plasma spraying a coating a mixed metal oxide onto an engine, exhaust-gas-system or powertrain component, wherein the coating contains a component that oxidizes hydrocarbons. In one embodiment, the component that oxidizes hydrocarbons prevents residue buildup. In one or more embodiments, the engine, exhaust-gas-system or powertrain component is selected from the group consisting of turbocharger, valve, piston, piston fireland, firedeck, compressor housing, intake port, injection nozzle, shroud, swirl generator, combustion chamber and combinations thereof.

In one or more other embodiments, a surface of the engine, exhaust-gas-system or powertrain component that is prone to residue buildup is sprayed. In other embodiments still, the coating comprises a mixed metal oxide, the mixed metal oxide comprising at least two metals selected from the group consisting of Al, Ti, Ce, Pr, La, Y, Nd, Mn and combinations thereof. In another variant, the coating further comprises a precious metal. In a further embodiment, the precious metal comprises Pd. In yet another embodiment, the coating is catalytically active to remove carbonization residue.

A second aspect of the invention pertains to a method of applying a coating to an engine, exhaust-gas-system or powertrain component. The method comprises suspension plasma spraying a coating onto an engine, exhaust-gas-system or powertrain component, wherein the coating comprises a mixed metal oxide comprising at least two metals selected from the group consisting of Al, Ti, Ce, Pr, La, Y, Nd, Mn, Zr and combinations thereof. In one embodiment, the coating is catalytically active for the oxidation of hydrocarbons. In another embodiment, the engine, exhaust-gas-system or powertrain component is selected from the group consisting of turbocharger, valve, piston, piston fireland, firedeck, compressor housing, intake port, injection nozzle, combustion chamber and combinations thereof. In yet another embodiment, a surface of the engine, exhaust-gas-system or powertrain component that is prone to residue buildup is sprayed.

A third aspect of the invention pertains to a method of applying a coating to an engine, exhaust-gas-system or powertrain component. The method comprises forming a suspension by dispersing mixed metal oxide particles in a liquid, feeding and injecting the suspension into a plasma torch or plume, and plasma spraying of the suspension towards the surface of an engine, exhaust-gas-system or powertrain component. In one embodiment, the suspension plasma is sprayed onto a surface of the engine, exhaust-gas-system or powertrain component that is prone to residue buildup. In another embodiment, the mixed metal oxide comprises at least two metals selected from the group consisting of Al, Ti, Ce, Pr, La, Y, Nd, Mn, Zr and combinations thereof. In a further embodiment of this aspect, forming a suspension further comprises dispersing a precious metal in the liquid. In another embodiment, the precious metal comprises Pd.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an SEM image of a cross section of a suspension plasma coating applied to a substrate in accordance with one or more embodiments of the invention; and

FIGS. 2-9 show graphical data of several samples applied by various coating techniques.

DETAILED DESCRIPTION

Before describing several exemplary embodiments of the invention, it is to be understood that the invention is not limited to the details of construction or process steps set forth in the following description. The invention is capable of other embodiments and of being practiced or being carried out in various ways.

Residue buildup occurs as a result from unburned hydrocarbons, lubricant oil and soot. The problem of residue buildup can occur on the surfaces of various engine, exhaust gas system and powertrain components. This includes, but is not limited to the turbocharger, valve, piston, piston fireland, fire deck, compressor housing, intake port, injection nozzle, shroud, swirl generator and combustion chamber.

One aspect of the invention relates to a coating that prevents deposit buildup on engine and powertrain components. An embodiment of the invention pertains to an article component comprising an engine or powertrain component and a coating applied to the engine or powertrain component.

Without a coating, the engine or powertrain component would have at least some of its surface exposed to hydrocarbons. The coating comprises a mixed metal oxide, which is comprised of at least two metals selected from the group consisting of Al, Ti, Ce, Pr, La, Y, Nd, Zr and Mn. In another embodiment, the coating also comprises a precious metal. In yet another embodiment, the coating is catalytically active to the oxidation of hydrocarbons. In a specific embodiment, the coating comprises Pd and another component selected from those provided above.

Another aspect of the invention relates to methods for applying the coating described herein using a suspension plasma spray. In a specific embodiment, the invention pertains to a method of applying a coating to an engine, exhaust-gas-system or powertrain component, the method comprising suspension plasma spraying a coating onto an engine, exhaust-gas-system or powertrain component, wherein the coating oxidizes hydrocarbons to prevent residue buildup. In a further embodiment, standard catalytic wash coat slurry is used. This can be used to obtain a durable high-surface area coating that prevents deposit buildup.

In one or more embodiments, the technique for coating the catalytic powder to the surface of the component. Standard plasma spray techniques significantly reduce surface area and thus diminish the catalytic activity of the material. Typical washcoat techniques suffer from insufficient durability of the coating. Suspension plasma spray coating provides a solution as it provides high surface area coatings with strong durability at the same time. One or more embodiments of the suspension plasma techniques described herein provide several advantages not yet addressed in the prior art. For example, the coatings applied via suspension plasma spraying exhibit much more stability as compared to air spray coatings. Additionally, such suspension plasma spray coatings exhibit more catalytic activity than conventional plasma spray techniques. Yet another advantage is that it can be difficult to apply precious metals using conventional plasma techniques, but much easier using suspension plasma.

A related embodiment pertains to a method of applying a coating to an engine, exhaust-gas-system or powertrain component, the method comprising suspension plasma spraying a coating onto an engine, exhaust-gas-system or powertrain component, wherein the coating comprises a mixed metal oxide comprising at least two metals selected from the group consisting of Al, Ti, Ce, Pr, La, Y, Nd, Mn, Zr and combinations thereof. In a specific embodiment, only the surface of the engine, exhaust-gas-system or powertrain component that is prone to residue buildup is sprayed. In one or more embodiments, the component has grooves or indentations on the surface of the component. In another embodiment, the coating also comprises a precious metal, for example, Pt, Pd, Rh and/or Au. In a specific embodiment, the precious metal comprises Pd. In one or more embodiments, the coating is catalytically active to remove hydrocarbon deposits on engine components. In a specific embodiment, the coating comprises Pd and another component selected from those provided above. In another embodiment, a post-deposition or post-impregnation process may be used to enhance the coating. In order to reduce the overall precious metal content of the coating, post-impregnation can be used such that the precious metal would be present at the surface only. The other ceramic layer would only provide the surface adhesion to the metal, like a bond coat. One advantage of one or more of the suspension spray coatings described herein is the ability to apply the full coating in a single step, even those containing precious metal.

A third aspect of the invention relates to a method of applying a coating to an engine, exhaust-gas-system or powertrain component, the method comprising: suspending a mixed metal oxide in a suspension; atomizing the slurry with suspended mixed metal oxide into a suspension plasma as described further below; and spraying the suspension plasma onto a engine, exhaust-gas-system or powertrain component. Optionally, the suspension plasma may be sprayed only onto the surface of the engine, exhaust-gas-system or powertrain component that is prone to residue buildup. The mixed metal oxide may comprise at least two metals selected from the group consisting of Al, Ti, Ce, Pr, La, Y, Nd, Zr and Mn.

According to one or more embodiments, the metal oxides are in particulate form. In specific embodiments, particles of high surface area, e.g., from about 100 to 500 square meters per gram (“m²/g”) surface area, specifically from about 150 to 450 m²/g, more specifically from about 200 to 400 m²/g, are desired so as to better disperse the catalytic metal component or components thereon. The first layer refractory metal oxide also desirably is mesoporous and has a high porosity of pores up to 1456 Angstroms radius, e.g., from about 0.75 to 1.5 cubic centimeters per gram (“cc/g”), specifically from about 0.9 to 1.2 cc/g, and a pore size range of at least about 50% of the porosity being provided by pores of 50 to 1000 Angstroms in radius. For alumina particles, it may be desirable to utilize a high surface area mesoporous gamma alumina, for example GA-200.

Exemplary suspension plasma spray methods according to one or more embodiments involve several process steps. First, solid particles are dispersed into a liquid and kept in suspension during the process. Second, the suspension is fed and injected into a heat source. Next, the solid particles in suspension are at least partially melted and impact on a surface of an article to form a deposit. The heat source in plasma spraying can include, but is not limited to electric arc plasma, RF plasma or microwave plasma. Suitable examples of suspension plasma spraying are described in U.S. Pat. Nos. 5,609,921, 6,277,448, and 4,376,010, the entire content of each patent being incorporated herein by reference.

Suspension plasma spraying, according to one or more embodiments, involves a plasma spray deposition method for producing a material deposit onto a substrate. The method can comprise producing a plasma discharge; providing a suspension of a material to be deposited, this suspension comprising small solid particles of that material dispersed into a liquid or semi-liquid carrier substance; atomizing the suspension into a stream of fine droplets and injecting the stream of fine droplets within the plasma discharge; and by means of the plasma discharge, (a) vaporizing the carrier substance, (b) agglomerating the small particles into at least partially melted drops, (c) accelerating these drops, and (d) projecting the accelerated drops onto the substrate to form the material deposit.

The probe atomizes the suspension into a stream of fine droplets and injects this stream of droplets generally centrally of the plasma discharge. The suspension is then sheared and thereby atomized, and injected in the plasma discharge under the form of fine droplets through the opening. Although an example of suspension plasma spraying process and apparatus have been described hereinabove, the present invention is not limited to the process as apparatus described, and alternative atomizing processes are available to shear the suspension.

The stream of fine droplets travels through the plasma discharge to reach the substrate. As the droplets of suspension travel from the opening to the substrate, these droplets are subjected to several physicochemical transformations. The suspension is typically composed of small solid particles suspended and dispersed into a solvent or other liquid or semi-liquid carrier substance. When the fine droplets of suspension reach the plasma discharge, the solvent first evaporates and the vapor thus formed decomposes under the extreme heat of the plasma. The remaining aerosol of small solid particles then agglomerate into drops which are either totally or partially melted and/or vaporized. The plasma discharge accelerates the molten drops, which accumulate kinetic energy. Carried by this kinetic energy, the drops hit the substrate. The plurality of drops form on the substrate a layer of partially or totally melted drops partially overlapping one another.

In another example of a suspension plasma spray process, a solid-liquid state suspension is prepared in which solid particles with appropriate particle sizes are selected or processed. Suitable particle sizes are in the range of nano-meters to micron-meters, preferably less than one micron. If necessary, the particle sizes can be reduced in a high energy process, such as ball milling. If multiple supports are used, then this step is repeated as many times as necessary to achieve the desired final slurry (suspension) composition. A few additives may be added in very small quantities to achieve the required properties for coating, such as: binders, defoamers, suspension agents, and anti-microbials. Then, the solid particles are dispersed into a liquid, for example, by using mechanical agitation manner such as with a stirrer or circulating pump. The particles should be suspended well and uniform during suspension preparation and plasma spraying. Before use, a suspension will be checked for solids % content and adjusted if necessary for the coating method. Depending on the degree of settling during storage, a suspension may be stirred or agitated before coating.

The suspension is delivered from a storage container to an injection device which is aligned a plasma torch, for example, in vertical alignment. The feeding and injection of the suspension is controlled by parameters such as flow rate and delivery pressure. While the suspension is injected and penetrated into the plasma torch/plume, the liquid is vaporized and the solid particles are heated and at least melted partially. Directed by the dynamic force of the plasma torch, the melted particles are directed toward a substrate and finally deposit on the surface of the substrate. Plasma spray parameters can affect the properties of the deposited material. Such parameters include but are not limited to plasma working gases and their compositions, pressure and flow rate, plasma power and the distance between the suspension injection location and the surface of the article.

According to an embodiment of the invention, suspension plasma spraying can be to apply adherent, catalytic coatings to any metallic surface such as aluminum or various steels. Compared to traditional dip coating processes, limited material types can be used to provide adherent coatings, such as ceramic or fecralloy substrates. By using suspension plasma spraying, a wider variety of substrates can be utilized.

The application process may be used to apply a protective coating to any deposit-prone engine or powertrain component or surface thereof. This includes, but is not limited to, the turbocharger, valve, piston, piston fireland, firedeck, compressor housing, intake port, injection nozzle and combustion chamber. In a specific embodiment, the coating is applied to a metallic surface of the engine or powertrain component.

EXAMPLES Example 1

A sample was prepared by suspension plasma spraying an alumina and ceria-based coating onto a sandblasted, stainless steel substrate. The exact composition of the coating was 30:70 ceria:alumina with 0.6 weight % platinum, which the platinum deposited onto the alumina. FIG. 1 is an SEM image of the coating in cross section with elemental mapping using EDS. FIG. 1 also shows the porosity of the coating, which is shown as the black areas. The suspension plasma coated sample showed extraordinary durability. The sample was subjected to thermal-shock stress methods—4-h of lab aging, cycling through 30 seconds of heat (900° C.±20° C. flame exhaust) followed by 30 seconds in 110° C. cooling air—and no signs of degradation or cracks are visible as shown in FIG. 1. In addition to mechanical durability, the suspension plasma spray coated sample showed a high catalytic durability. In repeated tests, the samples retained their catalytic activity and no aging of the catalyst (as determined signal decrease) could be found when repeating the measurement at least 10 times. The SEM image demonstrates how the coating remains adhered, even after treatment, and does not even show any visible cracking.

Examples 2A (Comparative) and 2B

Examples 2A and 2B both comprised a 50:50 molar ratio on a metals basis of Al₂O₃:CeO₂. Prior to mixing the alumina and ceria, 0.20 wt % Pt was added to the ceria. Example 2A was applied via an air spray technique onto a test planchette, and is considered comparative because of its application method. Example 2B was applied via suspension plasma spraying.

Examples 3A (Comparative) and 3B

Examples 3A and 3B both comprised a 50:50 molar ratio on a metals basis of Al2O3:CeO2. Prior to mixing the alumina and ceria, 0.45 wt % Pt was added to the ceria, and 0.15 wt % Pt was added to the alumina, for a total Pt content of 0.6 wt %. Example 3A was applied via an air spray technique onto a test planchette, and is considered comparative because of its application method. Example 3B was applied via suspension plasma spraying.

Examples 4A (Comparative) and 4B

Examples 4A and 4B both comprised a 50:50 molar ratio on a metals basis of Al2O3:CeO2. Prior to mixing the alumina and ceria, 0.60 wt % Pt was added to the alumina. Example 4A was applied via an air spray technique onto a test planchette, and is considered comparative because of its application method. Example 4B was applied via suspension plasma spraying.

For all examples 2-4, on the planchette, soot and oil were applied to the surface, and a temperature ramp was applied in air. Combustion product CO and CO₂ development were measured. Planchettes with soot/oil mixture on the surface of the planchettes were placed in a furnace. The furnace was ramp in temperature at 15° K/min. The gas temperature right above the planchettes was measured by means of an additional type K thermocouple. The gases above the planchettes are extracted with a nozzle. This gas was analyzed for CO and CO₂ using an Uras 14, Advance Optima module from ABB which uses infrared light. From this measurement, the catalytic activity of the coating for hydrocarbon oxidation was deduced. The test was repeated 5 times for each test planchette. FIGS. 2A-B, 3A-B and 4A-B show the CO₂ signal for Examples 2A-B, 3A-B and 4A-B, respectively. Similarly, FIGS. 5A-B, 6A-B and 7A-B show the CO signal for Examples 2A-B, 3A-B and 4A-B, respectively. As can be seen in FIGS. 2-7, the samples applied via suspension plasma spraying performed at least as well as the samples applied via air spray. Whereas the signal for the suspension spray coatings stayed almost constant for all of the tests, the air-sprayed samples showed only a little aging (e.g. an increasing of the peak signal temperature of about 40° C. as compared to freshly prepared samples).

Example 5 Comparative

A coating comprising 100% ceria was applied onto a test planchette using a conventional plasma spray. It is considered comparative because of the method with which coating was applied.

Example 6 Comparative

A coating of pure aluminum was prepared on a test planchette. The test planchette consists of pure aluminum, and is free of any coating. It thus serves as a comparative example, and is representative of, for example, a turbocharger aluminum surface.

Example 7 Comparative

A coating comprising 100% ceria was applied onto a test planchette using an air spray technique. This is considered a comparative example because of the method with which the coating was applied.

Example 8 Comparative

A coating comprising 100% Zirconia was applied onto a test planchette using a conventional plasma spray technique. It is considered comparative because of the method with which coating was applied.

Testing of Comparative Examples 5-8

On the planchette, soot and oil were applied to the surface, and a temperature ramp was applied in air. Combustion product CO and CO₂ development were measured. Planchettes with soot/oil mixture on the surface of the planchettes were placed in a furnace. The furnace was ramp in temperature at 15 K/min. The gas temperature right above the planchettes was measured by means of an additional type K thermocouple. The gases above the planchettes are extracted with a nozzle. This gas was analyzed for CO and CO₂ using an Uras 14, Advance Optima module from ABB which uses infrared light. From this measurement, the catalytic activity of the coating for hydrocarbon oxidation was deduced.

In FIG. 8 the CO signal is displayed, and in FIG. 9 the CO₂ signal is shown. From FIGS. 8 and 9, it can clearly be seen that the ceria, when plasma sprayed, does not enhance the oxidation of the lube oil. The combustion activity is almost the same as for the catalytically inactive zirconia or a pure, uncoated aluminum surface. There is almost no CO₂ signal below 400° C., but a strong CO signal around 425° C. This means the combustion of the lube oil is incomplete, and residues (precursors for deposit buildup) continue to be burnt off around 425° C. In contrast, the air sprayed ceria shows a strong CO₂ signal around 325° C. and no CO peak around 425° C., meaning the lube oil burns off completely. That is, no residues or deposits will be left over. The signal above 500° C. stems in both cases from the carbon black initially applied onto the planchette.

While the air sprayed coating shows at least some catalytic activity, it has no durability, as shown in the previous examples. After a few tests, the coating will lose its activity and even peel off the surface. Thus, the most advantageous method is suspension spray, which has been shown to provide both, activity and durability.

Reference throughout this specification to “one embodiment,” “certain embodiments,” “one or more embodiments” or “an embodiment” means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrases such as “in one or more embodiments,” “in certain embodiments,” “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily referring to the same embodiment of the invention. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments.

Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It will be apparent to those skilled in the art that various modifications and variations can be made to the method and apparatus of the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention include modifications and variations that are within the scope of the appended claims and their equivalents. 

1. A method of applying a coating to an engine, exhaust-gas-system or powertrain component, the method comprising suspension plasma spraying a coating a mixed metal oxide onto an engine, exhaust-gas-system or powertrain component, wherein the coating contains a component that oxidizes hydrocarbons.
 2. The method of claim 1, wherein the component that oxidizes hydrocarbons prevents residue buildup.
 3. The method of claim 2, wherein the engine, exhaust-gas-system or powertrain component is selected from the group consisting of turbocharger, valve, piston, piston fireland, firedeck, compressor housing, intake port, injection nozzle, shroud, swirl generator, combustion chamber and combinations thereof.
 4. The method of claim 3, wherein a surface of the engine, exhaust-gas-system or powertrain component that is prone to residue buildup is sprayed.
 5. The method of claim 4, wherein the coating comprises a mixed metal oxide, the mixed metal oxide comprising at least two metals selected from the group consisting of Al, Ti, Ce, Pr, La, Y, Nd, Mn and combinations thereof.
 6. The method of claim 5, wherein the coating further comprises a precious metal.
 7. The method of claim 6, wherein the precious metal comprises Pd.
 8. The method of claim 1, wherein the coating is catalytically active to remove carbonization residue.
 9. A method of applying a coating to an engine, exhaust-gas-system or powertrain component, the method comprising suspension plasma spraying a coating onto an engine, exhaust-gas-system or powertrain component, wherein the coating comprises a mixed metal oxide comprising at least two metals selected from the group consisting of Al, Ti, Ce, Pr, La, Y, Nd, Mn, Zr and combinations thereof.
 10. The method of claim 9, wherein the coating is catalytically active for the oxidation of hydrocarbons.
 11. The method of claim 9, wherein the engine, exhaust-gas-system or powertrain component is selected from the group consisting of turbocharger, valve, piston, piston fireland, firedeck, compressor housing, intake port, injection nozzle, combustion chamber and combinations thereof.
 12. The method of claim 11, wherein a surface of the engine, exhaust-gas-system or powertrain component that is prone to residue buildup is sprayed.
 13. A method of applying a coating to an engine, exhaust-gas-system or powertrain component, the method comprising: forming a suspension by dispersing mixed metal oxide particles in a liquid; feeding and injecting the suspension into a plasma torch or plume; and plasma spraying of the suspension towards the surface of an engine, exhaust-gas-system or powertrain component.
 14. The method of claim 13, wherein the suspension plasma is sprayed onto a surface of the engine, exhaust-gas-system or powertrain component that is prone to residue buildup.
 15. The method of claim 13, wherein the mixed metal oxide comprises at least two metals selected from the group consisting of Al, Ti, Ce, Pr, La, Y, Nd, Mn, Zr and combinations thereof.
 16. The method of claim 13, wherein forming a suspension further comprises dispersing a precious metal in the liquid.
 17. The method of claim 16, wherein the precious metal comprises Pd. 